No medication or perioperative treatment need be withheld or modified as a consequence of the patient being enrolled in the study. There is no requirement for starting any addition medication as a consequence of the study. Patients may withdraw at any time by withdrawal of consent, in which case all subject data will be destroyed and only the fact that consent was withdrawn will be documented. The anaesthetist with clinical responsibility for the patient may withdraw the patient from the study at any time, in which case the reason for withdrawal will be documented on the data collection form and any data collected will be kept until study completion.